The present application relates to systems and methods for pyrometry calibration, and more particularly relates to systems and methods for calibrating pyrometers for use in chemical vapor deposition systems using reflectivity and temperature measurements obtained from a eutectic calibration target.
Accurate temperature readings are essential for many industrial processes such as, for example, epitaxial growth of layers on wafers in susceptor-based chemical vapor deposition (“CVD”) systems. Uniform deposition in such systems is dependent on even temperature distribution along with other variables such as, for example, reactor pressure, reactant gas ratios, reactant gas flow rates, and the like. Thus, accurate in situ measurements of CVD reactor temperature are desirable. These temperature measurements preferably should be accurate enough to ensure uniform deposition of layers of material on wafers to be processed.
To measure temperature in CVD systems, a high temperature non-contact thermometry device such as a pyrometer may be employed. A pyrometer detects temperature by measurement of emissions from the internal surfaces of a CVD reactor.
To ensure the accuracy of pyrometer readings, though, the pyrometer should be properly calibrated to a temperature scale. Calibration devices can employ bonded thermocouples, emissivity detectors, and/or can employ these techniques in combination with calibration wafers that exhibit known properties at particular temperatures. In some pyrometer-based temperature measurement systems, calibration of the pyrometer sometimes requires that the pyrometry system be taken off-line - or in some circumstances even off-site during recalibration. Such off-site time or off-line time can result in decreased efficiency through lost processing time.
Some calibration systems employ a eutectic calibration wafer with a layer of material that melts into a eutectic at a known temperature. By measuring the temperature of the wafer using the pyrometer, and observing the layer to determine when melting occurs. These systems can be used to calibrate the pyrometer in place on the CVD apparatus, and can approximate the temperature of the melting and correlate the melting point of the eutectic to the measurements obtained by the pyrometer. For example, melting can be observed by monitoring reflectivity of the surface to detect the change in reflectance due to melting.
A problem with these systems as they currently exist is that the pyrometer is attempting to determine temperature readings from surfaces that typically have low emissivity because of their metal contents, making temperature difficult to read accurately.
Accuracy may also be reduced because at the point of melting of the eutectic wafer, other changes in phase, emissivity, and reflectivity may occur that could interfere with accurate temperature measurements and calibration. In addition, many eutectic wafers require a complex, many-layered design, raising quality control issues and making the wafers more expensive to produce.
What is needed is a pyrometer calibration system for a heated environment that solves these problems while providing accurate, simple, efficient and non-interruptive calibration of a pyrometer.